Method for oil-gas wells killing on deep water subsea deposits

FIELD: oil and gas industry.

SUBSTANCE: according to the method of oil-gas wells killing on deep water subsea deposits by pumping of certain volume of kill composition together with sea water into the well thus providing creation of killing spout in the well with timeless pressure on formation exceeding formation pressure not less than 1.2 times, as a killing composition, preventing immediate contact of cold sea water with overheated formation fluids and productive stratum of formation, large hydrophobic disperse system is used with density exceeding density of sea water more than 5 times in the volume ensuring in bottom-hole zone of the well creation of spout of large hydrophobic disperse system with height exceeding productive stratum formation opened by perforation not less than 3 times. Mentioned disperse system is a disperse system with volume of 70%, where as disperse medium hydrocarbon liquid is used, this liquid doesn't set solid under temperatures to -10C, its density is not less than 0.860 g/cm3; as disperse phase a mixture of hard metal balls with diameter within 1-2 mm is used, 50% of this ball mixture volume have fusion temperature well over bottom-hole temperature, and the other 50% of this ball mixture volume have fusion temperature 10C and more below bottom-hole temperature.

EFFECT: improving reliability of oil-gas wells killing on deep water subsea deposits with excessive temperature and pressure of productive formation.

3 cl, 2 tbl

 

The invention relates to the oil and gas industry, in particular to methods of killing exploration or development of oil and gas wells in the oil fields, reservoir whose effective thickness in the range of 50-200 m, open in the Gulf of Mexico at depths of about 1500 m and more occurring in the earth's crust at depths within 5500-6500 m

Under such conditions, the development of deepwater offshore oil and gas fields in the selection process of killing the well must be considered abnormally high temperature (300C) and pressure (600 MPa or more), which are inherent in each reservoir hydrocarbons, occurring in the earth's crust below the sea bottom at these depths.

Mostly for killing such an abnormally deep oil and gas wells with a barrel length dive to the bottom of the sea, 1500 m and the crust of the earth at 5500 m and more use normal sea water, providing for the establishment in the well bore back pressure on the producing formation, prepective pressure is 1.2 times or more, which, as practice shows, it is quite enough for plugging oil and gas wells, productive horizons which occur at depths of about 2500-4000 m and having a sheet temperature of about 80-120C and a pressure in the range of 250-350 bar.

Deep-sea oil and gas fields in the Gulf of Mexico the oil company, producing exploratory drilling or operation of oil fields, while jamming of oil and gas wells practice applying to the borehole bottom with sea water as the blocking material to seal the bottom hole not only the thickness of the production zone of the formation, but also the entire subsea wellbore, the addition of various components, weighting or thickening of sea water, such as high molecular weight polyelectrolytes, Cretaceous dispersions, suspensions of pieces of heavy mining of minerals with further cementing the stilling well.

The focus in such ways of killing the well is given to ensuring that the well pressure on the reservoir created by the column of sea water, heavy and dense on the bottom of a well specified components, exceed the formation pressure to values of about 1.15-1.20 and would not happen in time reduction in the well of the height of the liquid column plugging in the result for the column flow in the borehole or absorption on the bottom cracks or pores of the formation.

The drawback of such methods of killing the well is the fact that in their application are not taken into account the above features deep-water oil and gas fields, namely not taken any measures to prevent direct contact injected into the well of the cold sea the water, heavy or thickened above components, with overheated up to 300C and higher hydrocarbon fluid reservoir under the pressure of 600 MPa or more.

In the process of injection into a well with a total depth of the wellbore within 7500-8200 m is almost impossible to consider at what depth and at what temperature and pressure in the well will contact sea water or weighted and thickened sadavoy compositions based on it with overheated formation fluids and get to the bottom of a well specified shiawassee compositions in the form in which they are initially pumped into the well, and isn't in the hole "explosive" the process of turning sea water into the vapor state before entering it on the bottom of a well.

As the practice of plugging oil and gas wells in deepwater fields in the Gulf of Mexico, very often muted well, after a certain period of time after the killing, start to "react", i.e. from plugged wells in the sea is the allocation of a significant amount of gaseous and liquid hydrocarbons.

The explanation of these cases, only the result of the data on wells for their construction, poor cementing casing is not sufficient, since they do not explain the causes of p. the data and the methods of killing "explosive" nature of the emissions from the silenced wells compositions killing and petroleum hydrocarbons sometimes it caused the emergence of offshore fires and major oil spills.

So according to information from the U.S. coast guard in 2010, prior to the adoption by the United States government 6 month ban on exploratory drilling and operation of deepwater oil and gas fields in the Gulf of Mexico, occurred more than 900 cases of explosive emission and fires on offshore platforms in the process of plugging oil and gas wells.

Known combined methods of plugging oil and gas wells using as sadavoy compositions inverse emulsions (emulsions water in oil") with a density greater than the density of the formation water or water-salt solution, is used as the liquid plugging of wells, which provides for the settlement of such hydrophobic emulsion on the bottom hole reliable isolation of the productive formation from infiltration of fluid damping and successful process of killing wells (Composition and method of preparation of the inverse emulsion in a combined technology of killing wells. Patent No. 2156269, 2000).

If taken as an analogue of the proposed method this combined technology of killing the well, then used it as a blocking composition hydrophobic emulsion with a density of 0.05-01 g/cm3greater than the density of the line is used for plugging of water wells, due to its low stability at the temperature at the bottom hole of more than 100C, excludes the possibility of its use in the killing of wells in the Gulf of Mexico, where the temperature at the bottom of the wells, depending on the depth of the productive horizons range 150-350C.

In contrast to the known hydrophobic sadavoy compositions in the proposed method of plugging oil and gas wells in deep-sea deposits as zajavochnogo composition using hydrophobic dispersed system with a density greater than the density of sea water at least 5 times to the extent that the bottom-hole formation stable in time, impervious to sea water and superheated hydrocarbon fluids zajavochnogo post, overlapping not less than 3 times perforated productive thickness of the layer.

When this offer as zajavochnogo composition, unparalleled hydrophobic disperse system represents 70%by volume of the dispersed system, where as the dispersion medium using a hydrocarbon liquid with a density of not less than 0,860 g/cm3and a boiling point in the range 340-360C, for example, diesel fuel, and as a dispersed phase, a mixture of solid metal balls with a diameter of 1-2 mm, which is 50% of the total metal is a mini-balls made of metal with a specific gravity of about 8 and a melting point of about 1000C. and the remaining 50% of the balls are made of fusible metal, such as lead with a melting point of 330C. or tin with a melting point of 235C, or an alloy consisting of 11 parts by weight of bismuth and 9 weight parts of lead, with a melting point of the alloy to about 125C.

The necessary amount of hard hydrophobic disperse system (VSDSused as zajavochnogo composition for the formation at the well bottom is impervious to sea water and superheated hydrocarbon fluids zajavochnogo post hydrophobic dispersed systems, in each case calculated by the formula (1):

where r is the radius of the borehole, m,

HSDS- the height of the bottom-hole zone of the well zajavochnogo post heavy hydrophobic disperse system, m, is calculated by the formula (2):

where - NPTPthe thickness of the productive series of the reservoir, m

In each case, depending on the temperature of the formation at the borehole bottom, subject to jamming of the proposed method, applied hydrophobic disperse system as a dispersed phase, a mixture of metal balls, of which one half (by volume) should be made of metal with a melting point much higher than the temperature of the layer, for example made of metal with which the melting temperature of 1000C or more, and the other half of the balls must be made of fusible metal or metal alloy with a melting point of the balls 10C or more below the temperature of the reservoir, which provides on hole transition of such balls from the solid to the molten liquid plastic condition.

With hydrophobic dispersion system at the well bottom will reduce the volume of the solid transition metal balls with a high melting temperature in the volume of melt generated from the beads with low melting point and highlight of the dispersed system is lighter than sea water, the dispersion medium diesel fuel that floats to the top of the well, and the rest on the bottom hole portion of the dispersed system is transformed into a column containing about 50% by volume of solid metal balls in a metal melt, which is formed from the beads with a melting temperature below the formation temperature at the bottom hole.

Thus, the share of such post-metal systems increases and becomes almost an order of magnitude greater specific weight of sea water.

The presence of a well bore zone of such high-viscosity heavy metal pillar having a high adhesion to the walls of the well height, overlapping perforated thickness productive the Lasta, allows to significantly improve the reliability of plugging oil and gas wells in deep-sea deposits with an abnormally high temperature and pressure of the reservoir.

Considering the fact that used in the proposed composition of the heavy hydrophobic disperse system as a dispersed phase metal balls are thermal conductivity, on average, two order higher than the conductivity of the extracted hydrocarbons and higher thermal conductivity of sea water, this property allows us to consider this system in the borehole between the cold sea water and overheated formation fluids, not only as a means of preventing their direct contact, but also as a temperature regulator, eliminating the conditions for the occurrence of explosive processes of vaporization in the borehole using sea water as the base fluid damping on the deep sea fields.

As an example, in table 1 and table 2 presents the possible composition and main characteristics of heavy hydrophobic disperse systems, which can be recommended when implementing the proposed method of plugging oil and gas wells in deepwater offshore fields in the Gulf of Mexico, depending on their formation temperature.

<> From the data of table 1 it follows that depending on the type of fusible metal used for the manufacture of 50% by volume of metal balls, the density of the formed hydrophobic dispersed systems can range from 5.6 to 7, with a melting point of 50% of the volume of balls in the dispersed phase can vary from 125 to 325C. From the data of table 2 it follows that for deep-sea oil and gas fields in the killing of wells with characteristics corresponding to the wells of the Gulf of Mexico, you can apply together with sea water the proposed composition of heavy hydrophobic disperse system in the volumes of injection within 17-25 m3.

This is achieved by the formation in the borehole column of kill fluid pressure in the reservoir exceeds the pressure is more than 1.2 times.

In addition, under the influence of high rock temperature at the bottom hole of the hydrophobic dispersed system, the formation of zajavochnogo post formed from a melt of metal balls with a melting point of 10C or more below the reservoir temperature therein to about 50% by volume of metal balls with a melting point of 1000C or more, i.e. significantly above stratiform temperature.

The formation of such a heavy, viscous-plastic metal stolbina the bottom hole, is impervious to sea water, and superheated hydrocarbon fluids increases the success of the process of plugging wells in deep-sea deposits and eliminates the conditions for the occurrence of explosive emission during the killing.

Table 1
Variations of the composition of heavy hydrophobic dispersionThe specific weight of the composition, kg/m3For plugging wells with reservoir temperature, C
Part - 1 Content, % volume6,5150-300
Diesel fuel...30,0
Metal balls with tPL1000C...35,0
Metal balls with tPL125C...35,
Part - 25,6250-300
Diesel fuel...30,0
Metal balls with tPL1000C...35,0
Metal balls with tPL235C...35,0
Part - 37,0 more than 340
Diesel fuel...30,0
Metal balls with tPL1000C to 35.0
Metal balls with tPL325C...35,0

1. Method of plugging oil and gas wells in deep-sea deposits by injection into the well with seawater certain amount zajavochnogo composition, ensuring the creation of well post killing with unchanging in time pressure in the reservoir exceeds the formation pressure is not less than 1.2 times, characterized in that as zajavochnogo composition that prevents direct contact with cold sea water with overheated formation fluids and productive thickness of a layer, use heavy hydrophobic dispersed system with a density greater than the density of sea water is more than 5 times, to the extent that education in a well bore zone post heavy hydrophobic dispersed system height exceeding perforated productive thickness of the layer is not less than 3 times specified disperse system represents 70%by volume of the dispersed system, where as the dispersion medium using a hydrocarbon liquid that does not harden at temperatures down to -10is, density of at least 0,860 g/cm3and as the dispersed phase, a mixture of solid metal balls with a diameter in the range of 1-2 mm, 50% of the volume of balls of this mixture have a melting temperature considerably above the temperature at the bottom hole, and the other 50% of the volume of this mixture balls - melting temperature lower than the temperature at the bottom hole of 10or more.

2. The process of killing according to claim 1, characterized in that the hydrocarbon liquid used diesel fuel, 50% of the volume of balls of this mixture have a melting point of 1000C or more, the other 50% of the volume of this mixture balls - fusible.

3. The process of killing according to claims 1 and 2, characterized in that the balls with a melting point of 1000C and more are discarded steel balls for ball bearings, and fusible balls made of lead with a melting point of 330C, or tin with a melting point of 235C, or fusible alloy consisting of 11 parts of bismuth and 9 parts of lead, with a melting point of 125C.



 

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